Known in the art is a percussion mechanism which includes a housing with an internal space wherein there is received a reciprocable piston which divides this internal space into a working stroke chamber and an idle stroke chamber. The housing of the mechanism is made in the form of a series combination of a cylinder, a fluid-distribution unit and a connection for connecting the mechanism to a source of pressurized fluid. A socket is made in the cylinder at the side of the free end, which accomodates a work-performing member, and an exhaust port is made centrally of the cylinder. The working stoke chamber includes a counterbore made in the internal surface of the cylinder which is adjacent to the distribution unit.
The piston of the mechanism has a blind central bore wherein there is received a tube fixed in the distribution unit with aid of a coupling sleeve. The internal surface of the central bore of the piston has made therein an annular passage which communicates via an inclined passage with the idle stroke chamber. The bottom zone of this bore freely communicates via a lateral passage with the exterior of the piston, which engages the internal surface of the cylinder. The distribution unit, the tube and the coupling sleeve jointly define a valve space accommodating a valve member made in the form of an elastic bush having a seat-engaging shoulder on the internal side of the bush, this seat-engaging shoulder adjoining the base of the bush, facing the piston. The external lateral surface of the elastic bush and the internal lateral surface of the distribution unit define therebetween an annular inlet slit. This inlet slit communicates on one side thereof, through openings of the distribution unit, with the working stroke chamber of the mechanism, and on the other side communicates via the valve space and the lateral openings in the bush with a supply space defined within the bush. Also communicating with the supply space of the bush is the axial passage of the tube received in the piston.
Upon the abovedescribed pneumatic percussion mechanism having been connected via the connection member to a source of pressurized fluid, the fluid fills the supply space and from there flows via the lateral openings in the bush, and the valve space, the inlet slit of the valve, the openings of the distribution unit, the working or forward stroke chamber and the exhaust port into the ambient atmosphere, while it flows via the tube, the annular passage and the inclined passage into the idle stroke chamber. Under the action of the pressure differential in the valve space and in the working stroke chamber, the elastic bush is spread to close the inlet slit.
The working fluid that has filled the working stroke chamber is withdrawn through the exhaust port into the ambient air, while the idle stroke chamber is being filled with the pressurized working fluid, whereby the piston is driven through the idle or return stroke. As the tube closes off the annular passage of the piston, the supply of the working fluid is cut off, and as the piston by its further motion clears the exhaust port, the fluid escapes through the exhaust port. By this time the lateral passage of the piston aligns with the annular counterbore of the cylinder, through which the pressurized working fluid enters the working stroke chamber from the central bore of thus piston, filling this chamber. The pressure drop across the elastic bush, i.e. the difference between the pressures acting upon the external and internal lateral surfaces thereof, decreases and, when it falls to a predetermined value, the inherent resilience of the elastic bush contracts the bush, whereby the inlet slit becomes open. The pressure within the working stroke chamber becomes equal to that in the supply space. The piston first halts, and then is driven through a working stroke. When the internal surface of the cylinder closes off the lateral passage in the piston, the working stroke chamber remains in communication with the supply space exclusively via the valve. As the piston moves further on, it clears the exhaust port, and the pressure in the forward or working stroke chamber drops. The pressure differential expands the valve to close off the inlet slit, and the working fluid escapes from the working chamber. By this moment the tube opens the annular passage of the piston, and the pressurized working fluid fills the idle stroke chamber. Following an impact against the work-performing member, the piston is driven through an idle stroke.
A disadvantage of the abovedescribed pneumatic percussion mechanism having its valve made in the form of an elastic bush with an internal seat-engaging shoulder is that the valve defines with the distribution unit only one inlet slit. This hampers the feed of a substantial amount of the working fluid into the chamber of the mechanism, and thus affects the energy of the impact and the output capacity of the mechanism. If it is necessary to increase the pressure in other chambers of the mechanism, e.g. in the idle stroke chamber, it would require as many valves as there are chambers into which the pressurized fluid is to be additionally supplied. This would complicate the design of the mechanism and impair its reliability.